tems biology and risk modeling, quantitative cancer risks to humans will therefore be more precisely estimated for various radiation exposure scenarios.
From a better understanding of the radiation spectra that the astronauts are predicted to experience, cancer risk models will identify those radiation types and energies that are the most significant and least precisely understood from a human-risk standpoint. This should guide the experimental biology research work, including possible future whole-animal studies. In this way the overall uncertainty in the estimated cancer risk to the astronauts can be minimized.
The knowledge with regard to latent cancer effects from radiation greatly exceeds that of other potential chronic effects, especially cardiovascular disease and central nervous system effects. Researchers are just beginning to realize the potential importance of these other effects in relation to radiation exposures. There is a great need to understand their biological effects so that risk estimation is possible with reasonable precision for both acute and chronic exposures. The committee is concerned that these emerging adverse health effects are not receiving appropriate attention by NASA.
The NASA Bioastronautics Roadmap (NASA, 2005), as well as the recent National Council on Radiation Protection and Measurements report (NCRP, 2006), provides worthwhile guidance to the research issues. There is just sufficient time to reduce the radiation risk uncertainties before the lunar mission, but not enough time to impact design for the first missions. Because of the much greater radiation risks associated with a journey to Mars, it is also essential that research be increased now in order to make rational decisions on the feasibility of such an endeavor. In order to meet these goals, ongoing cell and animal studies need to be expanded and oriented toward an understanding of the mechanisms responsible for radiation risk, including cancer as well as the noncancer risks thought capable of having a significant impact on astronaut health.
One of the key enablers to reducing this uncertainty is the NASA Space Radiation Laboratory (NSRL), located at the Department of Energy’s (DOE’s) Brookhaven National Laboratory (BNL). Its combination of atomic number, energy, and flux makes the NSRL unique because it provides nearly the full range of particles and energies that constitute GCR, at fluxes that can go from a few particles per square centimeter per second to 100 million particles per square centimeter per second. Furthermore, the NSRL facility is dedicated to providing several thousand hours of beam time exclusively for NASA. The National Research Council’s (NRC’s) Radiation Hazards to Crews of Interplanetary Missions (NRC, 1996) stated that 3 months of beam time per year would be required to make progress on high-priority research questions. There is one other heavy-ion facility in the world (the Schwerionen Synchrotron Accelerator in Darmstadt, Germany) that can deliver the same range of particles and energies as NSRL, but it is fully dedicated to nuclear physics and can provide only occasional beam for space radiation experiments. Another handful of facilities (such as the cyclotron at DOE’s Lawrence Berkeley National Laboratory, the Proton Therapy Facility at Loma Linda University, and the Heavy Ion Medical Accelerator in Chiba, Japan) deliver a partial range of particles and/or energies, but are also fully dedicated to physics or radiation therapy programs, with restricted availability for space science experiments. These other facilities may prove to be cost-effective in providing ions and beam time for certain classes of experiments, but they cannot be seen as a substitute for NSRL. Finally, because NSRL is almost fully dedicated to NASA service, space-specific modifications can be obtained that are not available elsewhere, such as broadband beams, rapid changes between beams (e.g., iron to protons), large beam spots, in-beam incubators, laboratory facilities for on-line biochemical analyses, animal holding facilities, and dosimetry and data-acquisition services.
DOE’s Brookhaven National Laboratory has an annual budget of $500 million. NSRL is a relatively small part of a much larger accelerator complex that serves the high-energy, the nuclear physics, and the heavy-ion physics communities. That support can be expected to last as long as the research conducted by these communities continues to be cutting edge and vital. However, accelerators can be and have been closed when the frontier of science moved elsewhere. If DOE determines that the research topics requiring BNL accelerators no longer are a priority, they will be shut down or reconfigured. It is impossible to predict if or when that might occur; however, a prudent strategy for NASA would be to assume that the BNL accelerators will not be available 15 to 20 years from now and plan accordingly.